Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
CaltechAUTHORS
Published September 1981 | public
Journal Article Metadata-only

Metal and Bi/Pb microdistribution studies of an L3 chondrite: their implications for a meteorite parent body

Woolum, Dorothy S.
Burnett, D. S. ORCID icon

Abstract

We find strong localizations (relative to bulk) of Bi and to a lesser extent Pb. in some of the kamacite grains in Khohar. Other kamacite grains show no such enrichments. There are distinctive and correlated differences in the Ni contents of the two kamacite populations, with the Bi/Pb-rich kamacite grains having consistently lower Ni levels (sometimes unusually low. ~ 2% Ni) than the Bi/Pb-poor kamacite, which typically have ~ 6–7% Ni. The Bi/Pb-rich kamacite grains are also distinguished on the basis of their etching behavior, exhibiting a highly reactive attack, which has not been observed previously and which we believe may be due to the fact that the Bi/Pb-rich kamacite is finely polycrystalline. We conclude that the trace element microdistributions were not established in the nebula. Nor is it likely that the enrichments occurred with slow cooling in the presence of a vapor phase during the kamacite-taenite phase transition. Rather, the Bi/Pb-rich kamacite most likely reflect the occurrence of a brief reheating episode (or episodes), which may have been shock-induced and which was followed by rapid cooling. We find fine-grained metal-sulfide intergrowths which testify to such a reheating event, and one likely candidate for the site of this event is a hot ejecta blanket at the parent body surface. Iron oxides are found in our Khohar sections. We believe that they are not due to terrestrial alteration, that they are magnetite and that the magnetite probably originated in the same dynamic event in which the Bi/Pb distributions were established. The present data do not allow us to confidently determine whether the event occurred prior to, during, or after the compaction of this meteorite, although the simplest interpretation of the data would indicate the first alternative. Bulk Bi data for Khohar has been used for inferring accretion temperatures and this now appears inappropriate.

Additional Information

© 1981 Pergamon Press Ltd. Received 19 August 1980, Accepted 8 May 1981, Available online 27 March 2003. The authors gratefully acknowledge the technical advice and support and the splendid cooperation we have enjoyed at the 88-in. cyclotron at the Lawrence Berkeley Lab; in particular, we wish to thank G. WELCH, whose beam scanner we used, H. HARRINGTON, H. WIEMAN. D. SCOTT, and especially RUTH MARY LARIMER. Laboratory assistance from RONALD MASCITELLI and JIM CONCA is also much appreciated. DSW enjoyed the hospitality of the Harvard Smithsonian Center for Astrophysics and the Physics Department and the Laboratory for Nuclear Science at MIT in the final stage of this work and particularly wants to thank JOHN WOOD and KAREN MOTYLEWSKI for their help and for the use of their electron microprobe and SEM. ALAN DUBROC and LOU ANN CORDELL cheerfully prepared this manuscript. We are indebted to M. PRINZ of the American Museum for the Khohar (KAM) sample; the KB section came from the Caltech meteorite collection. This research was made possible by NASA grant NSG 7314.

Additional details

Identifiers Funding Dates Caltech Custom Metadata
Created:
August 22, 2023
Modified:
October 23, 2023